1. Field of the Invention
The invention relates to denture-cleansing compositions and somewhat more particularly to denture-cleansing tablets and methods of manufacturing the same.
2. Prior Art
Denture-cleansing compositions for use in aqueous solutions to automatically clean dentures which comprise a mixture containing sodium hydrogen carbonate as a gas-forming agent, sodium polyphosphate as a calcium-bonding agent, additional organic calcium-bonding agents and acid carriers, caroates as oxidizing agents, surfactants in the form of alkyl or alkyl aryl sulfonates, alkyl benzene sulfonates and inert carriers (excipients) and lubricants (releasants) are known.
German Offenlegungsschrift (DOS) No. 2,357,720 discloses a two-layer denture-cleansing tablet wherein at least one of the layers is composed of a mixture containing the foregoing materials so that a formulation for a tablet contains 15 to 25 wt. % of sodium hydrogen carbonate, 8 to 15 wt. % of sodium hexametaphosphate and acid disodium pyrophosphate, at least 15 wt. % of citric acid, 2 to 6 wt. % of an ethylene diamine compound, 1 to 4 wt. % of a polymeric surface-active dye carrier having cleansing properties and a dye material, at least 0.5 wt. % of at least one surfactant, 1 to 4 wt. % of a relatively high molecular weight polyethylene glycol and 0.5 to 1.5 wt. % of peppermint or some other flavoring material so that the pH in a 1% solution of such composition in water is 6.5 to 7.0.
In general, in this known cleansing tablet formulation, ethylene diamine tetraacetate is utilized as a complexing agent for forming chelate-complexes for any metal ions present, the sodium hydrogen carbonate is utilized as a pH-stabilizing gas-forming agent, the sodium hexametaphosphate is utilized as a softening agent and the citric acid as a reducing, antimicrobial agent which also dissolves tartar and other foreign coatings on the teeth of the dentures being cleansed. The ethylene diamine tetraacetate in this formulation also has a softening and demineralizing effect as a result of the chelate formation and also aids in dissolving tartar and other foreign coatings on the dentures. The high molecular weight polyethylene glycol functions as an antimicrobial effervescing agent while the surfactants in general have an emulsifying effect and function to dissolve various foreign coatings on dentures as a result of their surface activity. Sodium pyrophosphate in this formulation functions as a reducing and softening agent and also dissolves various coatings on dentures due to the surface activity thereof. The caroates, i.e., salts of Caro's acid, are oxidizing agents. In the known cleansing tablet formulation, the polymeric dye carrier with surface-activity cleansing property is, preferably, a commercially available sodium salt of polycarboxylic acid (more fully described in the earlier cited DOS No. 2,357,720 at page 17, lines 15-16), which is said to also improve the cleansing action of the overall formulation. The alkyl benzene sulfonate used as a surfactant in this formulation is, for example, sodium dodecyl benzene sulfonate to which fatty acid disodium sulfosucciantes may also be added. The preferred molecular weight of the polyethylene glycol used in the known formulation may range between 4000 and 25,000 but is most preferably about 20,000.
Generally, the foregoing prior art denture-cleansing tablet formulation yields relatively good results. However, in many applications it is desirable to obtain a much shorter cleansing time than the about 10 to 15 minutes required with this prior art formulation. Further, the two-layer tablet structure disclosed by DOS No. 2,357,720 is relatively expensive to manufacture.
It is also known that deposits of calcium compounds on dentures or metal parts thereof or on jaw-regulating apparatuses can be more effectively dissolved or removed by special acid cleansing agents, such as described, for example, in Swiss Patent Specification No. 480,840, which, in a 1% aqueous solution, have a pH of 1.5 to 5. However, a disadvantage of these acid agents is that they inhibit the desired action of the chelate-forming complexing agents required in denture-cleansing formulations since such complexing agents cannot function at a pH below about 6.